Investment Securities - Gross Gains and Losses on Sales and Redemptions of Available for Sale Securities and Other Than Temporary Impairment Losses Recognized (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Sales and Redemptions of Available for Sale Securities:
Gross gains	$ 2,389	$ 2,439	$ 3,636
Gross losses	$ 0	$ 0	$ 230